Classroom Acoustics

Reverberation

Reverberation time (RT) is the amount of time it takes a steady state sound to decrease 60 dB from it peak amplitude  Reflected speech overlaps with the direct speech signal, but with a delay  covers up or masks softer speech elements  "muddies" vowel sounds (longer RT due to greater energy)  Unoccupied classroom reverberation should not surpass 0.6 seconds in smaller classrooms or 0.7 seconds in larger rooms

Minimal Hearing Loss denotes

lack of alarm, a feeling that the condition will have little impact  The use of the term mild or minimal can have a ripple effect beyond the parents  Physicians, teachers and other caregivers may have the impression that the hearing loss is not significant, and will thus require minimal attention or intervention McKay (2008) -It is up to the habilitationist to educate the parents and other care givers about the impact of mild or minimal hearing loss

Indoors reverberation

often becomes a factor before audibility is an issue

Architectural/Room acoustics

play a large roll in the amount of reverberation in a classroom.

To minimize noise level in classroom

 Install carpet  Apply rubber tips on chair/desk legs  Hang acoustic panels Bookshelves/wall dividers Window treatments  Arrange room so instruction occurs away from noise sources (i.e., AC vent)

Recommended equipment to have in classroom:

 Listener  Battery tester  Air blower  Extra supplies

classroom reverb

 NH listeners can tolerate an RT of 1s  HI listeners require RT of 0.4 to 0.5 Crandell et al. (2005)  Less than 1⁄2 of classrooms have a RT of 0.6 or less

Classroom Acoustics

 Noise tends to mask the weaker consonants considerably more than the stronger vowel sounds  Upward spread of masking  Noise avg. 50-60 dBA SPL in regular classroom  Avg speech = 65dB SPL  +5dB SNR  Students w/ NH need about +6dB SNR for optimal understanding!

Effects of SNR

 Research data suggests that +15 dB SNR should be provided for children with HL Unoccupied classroom noise must be no more than 35 dB(A) This is not achieved frequently (less than 30%)  Noisy rooms increase vocal stress on teachers

The Acoustic Speech Signal

 The distance from the speaker has a great effect on the level of the speech signal  The inverse square law: for every doubling of distance the amplitude of a sound decreases by 6 dB

Minimal Hearing Loss

 Unilateral and Mild Hearing Loss are often categorized as Minimal Hearing Loss  Both impact a child's ability to communicate and to achieve academically Mild HL Pure Tone AC Thresholds of 20-40 dB HL (PTA) HOWEVER in children even a loss of 15 dB HL has an effect on their communication ability and educational achievement

Teachers can use following strategies

 Use FM systems, appropriately  Use visual aids  Gain students' attention before speaking  Encourage all students to help minimize noise  Face students, avoid covering mouth  Be aware that student w/ HL cannot speechread/attend and perform another task that requires them to look away  Provide handouts to provide context cues for speechreading  Ensure student w/ HL has preferential seating

Words Recognition Scores with combination of SNR and RT measured in actual classrooms

When SNR is +12 and RT is 0.4 s NH children score only 83% HI children score 60% At 0 SNR and an RT of 1.2 s NH children score 30% HI children score 11%

 ANSI S12.6 Acoustical Standard

1. Unoccupied classroom levels must not exceed 35 dBA 2. The signal-to-noise ratio (the difference between the teacher's voice and the background noise) should be at least +15 dB at the child's ears. 3. Unoccupied classroom reverberation must not surpass 0.6 seconds in smaller classrooms or 0.7 seconds in larger rooms

ANSI S12.6 Acoustical Standard

Standard for classrooms acoustics is voluntary  Modification of current classrooms to meet the SNR and RT standards is often impossible due to expense  Efforts should be made to get as close as possible to these standards in any classroom serving HI children

Other terms that may be helpful in describing minimal hearing loss

 Educationally significant  Developmentally significant  Socially significant

Amplification and ALDs in the Classroom

 Hearing aids & FM systems most common, followed by CI

Incidence of Unilateral Hearing Loss

(UHL) is about 1/1000 in infants (Prieve et al, 2000)  3.2/1000 for NICU babies  0.41/1000 for well-baby nursery babies 54/1000 school aged children

Localization

Binaural advantages are minimized or lost -Interaural intensity and time cues can be lost

Binaural summation

Binaural advantages are minimized or lost increased perception of loudness when sound is heard by two normal hearing ears

Binaural release from masking (binaural squelch)

Binaural advantages are minimized or lost  Differences between ears are used to focus on signal of interest  Allows an individual with normal hearing to "filter out noise" by focusing on signal from ear with best SNR  Children are affected more than adults due to lack of language and knowledge to "fill in the gaps"

Improving Classroom Acoustics

Location of classroom  away from railroad  away from band room, gymnasium  Placement of landscaping outside of room to block street noise  Child should be within a few feet of the speaker  Minimize multiple talker situations